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Probing around a pin to find center
« on: March 23, 2014, 09:22:02 PM »
Hey everyone, name here is Pete.  Newbie to Mach 3, with a probing question.  I need to probe around the end of a .050 pin, and be able to the change tools, if needed, and drill a .0138 diameter hole on the end of that pin.  Just the other day I set up Mach 3 with the Autoleveller for probing PCB's to be able to mill them.  So far, it works great.  But I want to be able to do the same kind of thing with X and Y around the pin to find that tough center point.  Been doing it with a Microscope and then inputting the offset into Mach 3, but still is not accurate enough to get exact center most time of the time.  Thanks for any input, or even a link to a previous forum discussion.   

Offline RICH

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Re: Probing around a pin to find center
« Reply #1 on: March 24, 2014, 08:08:05 AM »
FWIW,
Drilling a #80 hole accurately can be challenging and one needs to be meticulous from start to finish.
I peck drill mine at very low feed rates on the lathe using a 18000 to 40000 rpm live drill on the carriage
 ( or could also use the sensitive drillpress i made). Spit is usd as the starting cutting fluid.
Use an extanded eye relief microscope to  monitor the drilling and initialy just dwell at contact for some
time to let the drill start the hole without bending the bit.

One should test some to know just how accurate they can drill through the material.  One can actualy check and monitor
the spindle runout, total runout, and alignment and end prep of the rod required. Adjust as required.

Only use good / high quality drills in the small sizes and inspect for proper sharpening of the drill.
You don't say how deep you want to drill. Again one should test how accurate they can deep hole drill so they know before they go.

RICH
Re: Probing around a pin to find center
« Reply #2 on: March 24, 2014, 09:11:56 AM »
Hey Rich, thanks for your info,

I don't have access to a lathe and that would probably make things a little easier, but would still have the issue of getting exact center of the pin I would think.  I have been able to drill with my mill fine by keeping the feed rates super slow, about .1" a minute.  Am using a pencil grinder as my motor, some 40-50000 rpm I suspect per the manual.  Loud but works fine. 

Still hoping I can get some help with probing x and y from four directions, working similar to how Autoleveller does with Z.

Thanks, 

Pete
Re: Probing around a pin to find center
« Reply #3 on: March 24, 2014, 12:05:20 PM »
If you have a circular probe, you can use "Lautard's Maneuver".  I haven't programmed this but it would be easy enough to do.  Steps are as follows.

1.  Set the probe approximately in line with but at the left of the pin at a Z level where it can contact the pin.  Make an X probing move until the probe contacts the pin. Lift the probe above the pin keeping X and Y fixed.

2.  Move the probe to the right by half the sum of the probe diameter and the pin diameter, and record the "X" value.

3.  Move the probe in the negative Y direction until it clears the pin, and lower it.  Make a probing move until it contacts the pin.  Lift the probe above the pin keeping X and Y fixed.

4.  Move the probe in the positive Y direction by half the sum of the probe and pin diameters and record the "Y" value.

Go to step (1), and repeat the process 2 or 3 times until the values of X and Y make no significant change.
Re: Probing around a pin to find center
« Reply #4 on: March 24, 2014, 02:25:45 PM »
Thanks JohnHaine,

I've tried "Lautard's Maneuver" only by sight, but not electrically, no repeatable or consistent successes.  Considered just using a multimeter to tone when contact was made.  At this scale doing it by sight is nearly impossible and the problems with both are the jogging to the pin and what is contact and what is a "crash", unperceivable at these small scales.  Jogging would have to be very slow or if done electrically by the PC, would be faster, no human delay or skittishness involved.   

I am unfamiliar with how to program something for Mach 3.   So far to do the autotool zero, works great, but to be able to do it for the other axis, I am not sure yet. 

Pete
Probing around a pin to find center
« Reply #5 on: March 24, 2014, 03:52:55 PM »
Pete, you can make an isolated probe of a known diameter that fits your spindle and use the probing input on Mach, just as I assume you are doing for height.  I use this all the time and the machine stops virtually instantly when the probe touches the work, no apparent problem with "microcrashing".  I must say that I haven't tried Lautard's manoeuvre because up to now I haven't had the need to centre on a disc.  It would also be possible to touch at 3 or more points round the pin, but the maths looks trickier.  I'll try to get a pick of my probe later.


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Offline RICH

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Re: Probing around a pin to find center
« Reply #6 on: March 24, 2014, 03:57:48 PM »
The smaller you get the harder it is to set things up. Good lighting and proper manification is imperative. I use Albrecht chucks for the small drills and are very accurate and repeatable.
 
Crack of light of can easily be seen with a magnifier or a 15 to 30x microscope.
You have more inaccuracy in locating center of something due to spindle / drill / chuck runout than touch off. So many times the center ilocation is a spit of the runout your dealing with. Sorry for being anal about this.

Using an MPG can provide for precise control of movement to touch off or locate a point. I manualy center when using the sensitive drill press. A dowel held properly in a precision vise and sharpened to a trued  point
or small bored hole into the end fo the dowel allows for easier setup location of the center.

 RICH

Offline BR549

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Re: Probing around a pin to find center
« Reply #7 on: March 27, 2014, 03:03:46 PM »
What you need is a "Center of BOSS" routine to drive the probe to the center of the pin(boss).

If you need help Email me and I can can send you a working copy of the routine.